1. Field of the Invention
The present invention relates to a method and system for fabrication of atomic cells and more particularly to a method for electrolytically releasing controlled amounts of free alkali metal into an atomic clock cell formed of a silicon wafer anodically bonded to glass layers
2. Description of Related Art
Miniature cells for atomic clocks have been formed by anodically bonding glass wafers to both sides of a silicon wafer, containing many small holes. Each of these small holes is destined to be a vapor cell. Many hundreds of cells can be mass produced on a single silicon wafer. Each cell can be integrated with, for example, a vertical cavity surface emitting laser (VCSEL), a photodetector, electronics, and a thermal control system.
Conventional methods have been used to fill the anodically bonded cells with Rb or Cs metal. In one method, small holes are opened through a glass window into each cell, for example with a focused laser, a small amount of liquid Cs or Rb metal is injected with a tiny syringe or an array of syringes, along with an appropriate mixture and pressure of buffer gases. The hole is then hermetically sealed.
In a second method, each cell is manufactured with a mixture of alkali-metal salt and reducing agents that can release the Cs or Rb metal into the cell after appropriate thermal processing. When the mixture is subsequently heated to several hundred degrees Celsius, the chemical components react releasing free alkali metal and nitrogen gas. It is not easy to control the gas composition in this process, and the cell can also be contaminated with reaction products, which can affect the vapor pressure of the alkali-metal atoms and can degrade the optical properties of the cell. Both methods appear to have limitations for scaling to mass production.
It is desirable to provide an improved method in which controlled amounts of alkali metal can be released into miniature cells using an electrolytic current which method can be used for mass production of cells with reduced manufacturing costs.